The speaker is thinking about someone who once meant everything and then hurt them badly. At first the language is playful and almost sweet: the person was "the peanut butter to my jelly" and "the apple to my eye." Those familiar phrases make the past love sound easy and comfortable. Then the tone shifts with a blunt "But now?" and the person shrinks into a painful memory. The speaker feels used, since they gave "my all" and got nothing honest back.
One neat turn comes when the memory becomes a "reality," and that reality is heartbreak itself. The ending is the sharpest part. Asking "Are you happy now?" sounds like a final goodbye, but "I sure hope so" is loaded with sarcasm and leftover hurt. The mood is bitter and raw, with a flicker of wounded pride. The speaker wants to seem like they are moving on, but the pain still shows through.